In general, organic LEDs (OLEDs) consist of a very thin layer (approx. 100 nm) of organic substances on a glass substrate covered with an electrically conducting but optically transparent oxide, usually indium-tin oxide (ITO). ITO forms the anode and a layer of aluminum (approx. 100 nm) evaporated on the organic layer stack forms the cathode. When a voltage of typically 2 to 10 volts is applied between anode and cathode, the organic stack emits light.
However, most of the light generated in the OLED is not able to escape from the substrate into the air, due to waveguiding in the organic layers or in the glass. A better light extraction is therefore essential for an efficient operation of OLEDs.